FM / Tie

/usr/share/perl5/Tie

Name	Size	Mode	Actions
Array.pm	7318	0644	edit dl rm
File.pm	77444	0644	edit dl rm
Handle.pm	4202	0644	edit dl rm
Hash.pm	7639	0644	edit dl rm
Memoize.pm	4251	0644	edit dl rm
RefHash.pm	6237	0644	edit dl rm
Scalar.pm	4164	0644	edit dl rm
StdHandle.pm	1398	0644	edit dl rm
SubstrHash.pm	5404	0644	edit dl rm

Edit: /usr/share/perl5/Tie/Scalar.pm (4164B)

package Tie::Scalar;

our $VERSION = '1.04';

=head1 NAME

Tie::Scalar, Tie::StdScalar - base class definitions for tied scalars

=head1 SYNOPSIS

package NewScalar;
    require Tie::Scalar;

@ISA = qw(Tie::Scalar);

sub FETCH { ... }		# Provide a needed method
    sub TIESCALAR { ... }	# Overrides inherited method

package NewStdScalar;
    require Tie::Scalar;

@ISA = qw(Tie::StdScalar);

# All methods provided by default, so define
    # only what needs be overridden
    sub FETCH { ... }

package main;

tie $new_scalar, 'NewScalar';
    tie $new_std_scalar, 'NewStdScalar';

=head1 DESCRIPTION

This module provides some skeletal methods for scalar-tying classes. See
L<perltie> for a list of the functions required in tying a scalar to a
package. The basic B<Tie::Scalar> package provides a C<new> method, as well
as methods C<TIESCALAR>, C<FETCH> and C<STORE>. The B<Tie::StdScalar>
package provides all the methods specified in  L<perltie>. It inherits from
B<Tie::Scalar> and causes scalars tied to it to behave exactly like the
built-in scalars, allowing for selective overloading of methods. The C<new>
method is provided as a means of grandfathering, for classes that forget to
provide their own C<TIESCALAR> method.

For developers wishing to write their own tied-scalar classes, the methods
are summarized below. The L<perltie> section not only documents these, but
has sample code as well:

=over 4

=item TIESCALAR classname, LIST

The method invoked by the command C<tie $scalar, classname>. Associates a new
scalar instance with the specified class. C<LIST> would represent additional
arguments (along the lines of L<AnyDBM_File> and compatriots) needed to
complete the association.

=item FETCH this

Retrieve the value of the tied scalar referenced by I<this>.

=item STORE this, value

Store data I<value> in the tied scalar referenced by I<this>.

=item DESTROY this

Free the storage associated with the tied scalar referenced by I<this>.
This is rarely needed, as Perl manages its memory quite well. But the
option exists, should a class wish to perform specific actions upon the
destruction of an instance.

=back

=head2 Tie::Scalar vs Tie::StdScalar

C<< Tie::Scalar >> provides all the necessary methods, but one should realize
they do not do anything useful. Calling C<< Tie::Scalar::FETCH >> or 
C<< Tie::Scalar::STORE >> results in a (trappable) croak. And if you inherit
from C<< Tie::Scalar >>, you I<must> provide either a C<< new >> or a
C<< TIESCALAR >> method.

If you are looking for a class that does everything for you you don't
define yourself, use the C<< Tie::StdScalar >> class, not the
C<< Tie::Scalar >> one.

=head1 MORE INFORMATION

The L<perltie> section uses a good example of tying scalars by associating
process IDs with priority.

=cut

use Carp;
use warnings::register;

sub new {
    my $pkg = shift;
    $pkg->TIESCALAR(@_);
}

# "Grandfather" the new, a la Tie::Hash

sub TIESCALAR {
    my $pkg = shift;
    my $pkg_new = $pkg -> can ('new');

if ($pkg_new and $pkg ne __PACKAGE__) {
        my $my_new = __PACKAGE__ -> can ('new');
        if ($pkg_new == $my_new) {  
            #
            # Prevent recursion
            #
            croak "$pkg must define either a TIESCALAR() or a new() method";
        }

warnings::warnif ("WARNING: calling ${pkg}->new since " .
                          "${pkg}->TIESCALAR is missing");
	$pkg -> new (@_);
    }
    else {
	croak "$pkg doesn't define a TIESCALAR method";
    }
}

sub FETCH {
    my $pkg = ref $_[0];
    croak "$pkg doesn't define a FETCH method";
}

sub STORE {
    my $pkg = ref $_[0];
    croak "$pkg doesn't define a STORE method";
}

#
# The Tie::StdScalar package provides scalars that behave exactly like
# Perl's built-in scalars. Good base to inherit from, if you're only going to
# tweak a small bit.
#
package Tie::StdScalar;
@ISA = qw(Tie::Scalar);

sub TIESCALAR {
    my $class = shift;
    my $instance = @_ ? shift : undef;
    return bless \$instance => $class;
}

sub FETCH {
    return ${$_[0]};
}

sub STORE {
    ${$_[0]} = $_[1];
}

sub DESTROY {
    undef ${$_[0]};
}

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